This application is in response to an NIH FOA inviting applications for projects to identify and qualify extracellular RNA (exRNA)-based biomarkers derived from human body fluids to diagnose and monitor disease progression and response to therapy. We propose to identify and validate candidate circulating miroRNAs in well-defined multiple sclerosis (MS) patient populations. Studies using existing human biospecimen collections were strongly encouraged by the NIH FOA and for the UH2 phase we will take advantage of a unique resource termed CLIMB (Comprehensive Longitudinal Investigation of Multiple Sclerosis at Brigham and Women's Hospital). CLIMB is a cohort of over 2000 MS patients that began enrollment 12 years ago and includes yearly blood samples, clinical exams and quantitative MRI imaging. We present preliminary data that we can indeed measure circulating miRNAs in our MS cohort and have found links to disease stage, response to therapy and disability. For the UH3 phase we have identified valuable sources of blood samples from both academic and pharmaceutical collaborators that will be used to validate our UH2 findings and provide the basis for the use of circulating miRNAs in the clinic. SPECIFIC AIMS FOR UH2 PHASE: 1) Identify miRNAs that will act as diagnostic biomarkers by comparing MS patients to healthy controls, patients with other neurological diseases and patients with other autoimmune diseases. 2) Identify disease stage miRNA biomarkers by comparing RRMS patients, SPMS patients and PPMS patients. 3) Identify prognostic miRNA biomarkers by determining the change in each miRNA over two years and assessing which miRNAs are sensitive to long-term change in disease status. 4) Identify treatment response miRNA biomarkers by comparing the baseline miRNA expression in responders and non- responders to treatment. 5) Identify disability miRNA biomarkers by correlating miRNAs with EDSS and MRI measures of disease status. SPECIFIC AIMS FOR UH3 PHASE: Circulating miRNAs identified in the UH2 phase will be extensively studied and we will address the following two aims: 1. Validation of miRNA biomarkers identified in the UH2 phase in well defined independent patient cohorts. 2. Determine which miRNAs identified in the UH2 phase can be used as preclinical disease biomarkers. We will take advantage of well characterized serum samples from a number of sources including: The SUMMIT International MS Consortium, the NIH sponsored CombiRx clinical trial, the Biogen Idec sponsored IMPACT trial, the Swedish EIMS epidemiologic investigation of MS, the Canadian Pediatric Demyelinating Disease Study and the GEMS (Genes and Environment MS study).